Factual note about the game (4)
I believe the answer is:
true
'factual' is the definition.
('true' can be similar in meaning to 'factual')
'note about the game' is the wordplay.
'note' becomes 'te' (**).
'about' means one lot of letters goes inside another.
'the game' becomes 'ru' (rugby union).
'te' placed around 'ru' is 'TRUE'.
(Other definitions for true that I've seen before include "Exact, factual" , "Straight or correct" , "Rightly so called" , "Factually accurate" , "Exact; faithful" .)